Many modern portable devices (e.g., laptop computers, mobile phones, digital cameras, video cameras, media players, personal digital assistants (PDAs), game console, etc.) include battery packs. One particular type of conventional battery pack includes one or more battery cells coupled to one or more Integrated Circuit (IC) chips. The chips typically include a controller (e.g., a microcontroller) and circuitry and provide, among other things, battery cell management and protection.
Some conventional battery packs include a Li-ion (Lithium ion) battery cell, which is essentially a volatile chemical reaction packaged inside a cylinder. Potential energy is stored in each cell, and if the battery cell is exposed to conditions outside of its specification the cell can over heat, catch fire or explode. Conventional battery packs configured with these volatile cells typically include fail-safe circuitry for detecting unsafe conditions (e.g., charge or discharge over-currents, short circuits, etc.), and for taking corrective action to prevent damage to the battery cell and/or device, and to protect the end user.
Conventional rechargeable batteries can be charged with a charger after discharge. When certain battery technologies (e.g., Li-ion and Lithium-polymer) are charged, constraints are placed on the charging system to avoid dangerous conditions. One such constraint relates to charging these cells when their cell voltages are below a certain level, what is commonly referred to as a Deep Under Voltage (DUV) condition. A deep under voltage condition can arise after deep discharge, or when the battery pack is charged for the first time. When charging cells from a deep under voltage condition, a lower than normal charge current is typically used for a period of time (i.e., a pre-charge period). After the cell voltage(s) have risen to a certain level, the charger can switch to a normal charge mode so as to minimize charge time for the cell(s). In a conventional system as described, the charger determines when the switch from pre-charge to normal or rapid charge should occur, based, primarily, on the cell(s) voltage level that it sees.
In some conventional battery packs, two external transistors (e.g., field effect transistor (FETs)) are connected in series with the battery cell(s) and are enabled and disabled to allow for the charge and discharge of the cells. The transistors allow the cell(s) to be disconnected from either the charger or the device based on one or more monitored conditions to avoid improper or dangerous operation. In one configuration, referred to as a high-side solution, the two transistors are coupled in series between the positive terminal of the cell(s) and a positive battery pack terminal (e.g., the external positive terminal interface to a device).